The development of Earth-abundant transition metal sulfide electrocatalysts with excellent activity and stability toward the alkaline hydrogen evolution reaction (HER) is critical but challenging. Iron-based sulfides are favored due to their economic benefits and good stability, but their intrinsic catalytic activity still needs to be improved urgently. Herein, we successfully prepared Fe9S10 nanosheet arrays on iron foam (Fe9S10/IF) through a simple one-step method and utilized plasma treatment to introduce S vacancies (Fe9S10-Vs/IF) to regulate their intrinsic catalytic activity. The final materials demonstrate excellent HER performance, and only need 149 mV to drive a current density of 10 mA cm-2 and a small Tafel slope of 50 mV dec-1. The experimental results show that the existence of S vacancies can enhance their intrinsic electrocatalytic activity. This work provides a reference value for the future regulation of iron-based sulfides and is devoted to the development of non-precious metal catalysts toward the HER.